How does the ‘bionic’ marathon suit work?

A paralysed woman has completed the London marathon with the aid of a robotic walking suit. But how does it work?

Claire Lomas, a 32-year-old former chiropractor who was paralysed from the chest down after being thrown from her horse in 2007, completed the London marathon with the aid of a robotic walking suit on Tuesday.

Designed by Israeli entrepreneur Amit Goffer, the £43,000 Rewalk suit – which has been termed “bionic” and “robocop” – enables people with lower-limb paralysis to sit, stand, walk and climb stairs.

Engineer Ian Cornwall, who works at Cyclone Technologies, a Yorkshire company which tests and develops the suit, explains how it works.

Backpack
The backpack contains a 28-volt lithium-ion battery, a back-up battery and an onboard computer, which drives the machine and contains a radio transmitter which communicates with the watch.
Batteries typically last about eight hours, and are rechargeable.
Cornwall says the computer programmes have lots of different parameters, and things such as the degree of tilt that activates the suit, the speed of the machine, and how long it waits before it moves forward between steps can be adjusted.

Motor tilt sensor
The entire machine relies on a single motion sensor, which propels the wearer’s legs forward by detecting shifts in balance and bodyweight.
The tilt sensor is worn in a pelvic brace on the left hand side of the body.
Leaning the upper body forward activates the sensor, which in turns sets the robotic legs in motion. The machine always sets off on the right foot.

Watch
The watch has buttons which enable the wearer to choose whether to sit, stand and ascend or descend stairs. The suit is put on in the sitting position, from which the only thing a person can do is stand.
However, the wearer has to assist the suit. If there was not enough assistance it would automatically fall back into the sitting position. Likewise if the wearer selects walk, but does not move his or her body, the suit would default back to the standing position. When it comes to ascending or descending stairs, the step height is pre-programmed in the computer, however all parameters can be altered.

Motor pods
Motor pods made of aluminium support body weight and keep the wearer rigid in the machine. There are also upper body straps for the same purpose.
The pods, strapped to the wearer’s upper and lower legs, contain small motors which execute movements and help rotate joints as well.

Footplates
Footplates are worn underneath the foot within the wearer’s trainers. They are made of strong carbon fibre, and carry the load of the equipment and the wearer.
Footplates can only support a person whose weight does not exceed 100kg.

Crutches
Crutches give the wearer balance as they lean forward. It is essential that wearers have enough strength in their hands and shoulders to be able to support crutches, as without them they would probably fall over.